1. Technical Field
The present invention relates to a method for manufacturing a molded foam.
2. Related Art
A molded foam is lightweight and excellent in rigidity, and therefore is utilized in various different fields for automobiles, aircrafts, vehicles and ships, architectural materials, electrical appliance housings, sports and leisure products, and the like.
According to one known method for manufacturing a molded foam, for example, polymer containing a thermoplastic resin as a main component is melted and kneaded in an extruder. Then, the resin is formed into a sheet shape by extruding through a circle-shaped die, and transferred by a transfer table. Subsequently, secondary foaming is performed by vacuum sucking the sheet-shaped resin using a vacuum suction apparatus to produce a molded foam (e.g., refer to Patent Document 1).
Further, there is known a method of obtaining a molded foam by providing a cylinder-shaped molded body including a thermoplastic resin foamed layer in a softened state (parison) between split mold blocks, clamping the split mold blocks with the cylinder-shaped molded body inserted therebetween, and compressing the cylinder-shaped molded body (e.g., refer to Patent Document 2, 3 or 4).
According to these methods, a molded foam is manufactured by blowing air into a parison and/or reducing a pressure between an outer surface of the parison and an internal surface of the mold block.
The documents that describe the related art are listed below.    Patent Document 1: JP 10-058533 A    Patent Document 2: JP 2003-236918 A    Patent Document 3: JP 2004-082332 A    Patent Document 4: JP 2004-284149 A
However, in the methods for manufacturing a molded foam described in Patent Documents 1 to 4, when a parison is inserted between split mold blocks without closely attaching a wall surface of the parison, a hollow portion (hereinafter referred to as “a hollow part”) can be easily formed within the parison. In this case, a structure of a molded foam 50 that is obtained partially includes a hollow part 51 as illustrated in FIG. 20. As a result, a strength (such as impact resistance) of the molded foam becomes insufficient.